The Synchronous Optical Network (Sonet) and Synchronous Digital Hierarchy (SDH) are standards for protocols for delivering digital data at high rates. These standards cover many of the layers of the OSI Reference Model.
The Sonet/SDH standards comprise a variety of signal rates, signal structures and mappings. An instrument that measures various parameters of a Sonet/SDH signal must be correctly configured to provide meaningful results.
Current Sonet/SDH test instruments require a user to know the current configuration of a Sonet/SDH signal in order to configure the instrument. However, in many test situations, the fact that a component of the signal is not as expected is what is causing communication problems and is why the instrument is needed. In such a case, the user must have a thorough knowledge of the Sonet/SDH standards and know why certain errors occur to properly configure the instrument.
There have been instrument that attempted to automate certain portions of an instrument's configuration. These automatic configurations operated at only a single layer of the Sonet/SDH signal hierarchy. For example, one instrument can determine the signal's data rate, but cannot determine the structure or the mapping. Another instrument assumes that it is correctly configured and automatically checks the specified tributary channels for error states.